(2015) Social grooming network in captive

Social grooming network in captive
chimpanzees: does the wild or captive
origin of group members affect sociality?
Marine Levé, Cédric Sueur, Odile Petit,
Tetsuro Matsuzawa & Satoshi Hirata
Primates
ISSN 0032-8332
Primates
DOI 10.1007/s10329-015-0494-y
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DOI 10.1007/s10329-015-0494-y
ORIGINAL ARTICLE
Social grooming network in captive chimpanzees: does the wild
or captive origin of group members affect sociality?
Marine Levé1 • Cédric Sueur2,3 • Odile Petit2,3 • Tetsuro Matsuzawa4,5
Satoshi Hirata6
•
Received: 28 August 2015 / Accepted: 6 September 2015
Ó Japan Monkey Centre and Springer Japan 2015
Abstract Many chimpanzees throughout the world are
housed in captivity, and there is an increasing effort to
recreate social groups by mixing individuals with captive
origins with those with wild origins. Captive origins may
entail restricted rearing conditions during early infant life,
including, for example, no maternal rearing and a limited
social life. Early rearing conditions have been linked with
differences in tool-use behavior between captive- and
wild-born chimpanzees. If physical cognition can be
impaired by non-natural rearing, what might be the consequences for social capacities? This study describes the
results of network analysis based on grooming interactions in chimpanzees with wild and captive origins living
in the Kumamoto Sanctuary in Kumamoto, Japan.
Grooming is a complex social activity occupying up to
25 % of chimpanzees’ waking hours and plays a role in
the emergence and maintenance of social relationships.
We assessed whether the social centralities and roles of
chimpanzees might be affected by their origin (captive vs
wild). We found that captive- and wild-origin chimpanzees did not differ in their grooming behavior, but that
& Satoshi Hirata
hirata.satoshi.8z@kyoto-u.ac.jp
1
Ecole normale supérieure, Paris, France
2
Département Ecologie, Physiologie et Ethologie, Centre
National de la Recherche Scientifique, Strasbourg, France
3
Institut Pluridisciplinaire Hubert Curien, Université de
Strasbourg, Strasbourg, France
4
Primate Research Institute, Kyoto University, Aichi, Japan
5
Japan Monkey Centre, Aichi, Japan
6
Kumamoto Sanctuary, Wildlife Research Center, Kyoto
University, 990 Ohtao, Misumi, Uki, Kumamoto 869-3201,
Japan
theoretical removal of individuals from the network had
differing impacts depending on the origin of the individual. Contrary to findings that non-natural early rearing
has long-term effects on physical cognition, living in
social groups seems to compensate for the negative
effects of non-natural early rearing. Social network analysis (SNA) and, in particular, theoretical removal analysis, were able to highlight differences between individuals
that would have been impossible to show using classical
methods. The social environment of captive animals is
important to their well-being, and we are only beginning
to understand how SNA might help to enhance animal
welfare.
Keywords Pan troglodytes Social network analysis Grooming Early rearing differences Behavioral
development Well-being
Introduction
Due to their phylogenetic similarity to humans, chimpanzees (Pan troglodytes) have attracted attention from
both zoos and researchers, and hundreds of individuals
have been brought into captivity from their African habitats
(Goodall and Peterson 1993). As a social species, chimpanzees live in groups of several members (Inskipp 2005).
Chimpanzee societies, which are known for their complexity, are demanding in terms of social cognition. They
display fission–fusion dynamics (Aureli et al. 2008),
wherein the community splits into smaller subgroups during one or even several days (Nishida 1968). Despite this,
community cohesion and social bonds among members are
maintained. The social network of the community is thus
complex (Shimada and Sueur 2014), with some individuals
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playing central roles in the collective social life (Kanngiesser et al. 2011).
In captivity, group members may arrive from other
places where they were also captive; they may be born into
captivity, or they may have come from the wild. The early
rearing of captive infant chimpanzees is not always performed by the mother, whereas the infant stays very close
to its mother for the first 2 or 3 years in the wild (Bard
1995). It is thought that normal behavioral development
depends, in part, on the early circumstances of the infant.
Severe sensory and social isolation during these formative
years results in behavioral consequences, reducing the
individuals’ ability to live in social groups, copulate, and
raise infants of their own (Bloomsmith et al. 2006).
Nursery-reared chimpanzees show more frequent abnormal
behaviors than their maternally reared counterparts (Ross
2003; Bloomsmith and Haberstroh 1995), have reduced
sexual and maternal abilities (Brent et al. 1996), and are
less likely to reproduce as adults (King and Mellen 1994).
The physical cognition of nursery-reared chimpanzees is
also impaired: they have reduced problem-solving skills
(Brent et al. 1995), and seem to show less adaptive
behavior than their wild-born counterparts (Morimura and
Mori 2010). In addition, this impairment may extend to
social aspects of their behavior, as behaviors such as tool
use are usually learned through social learning during
infancy both in the wild and in captivity (Biro et al. 2003;
Hirata and Celli 2003; Matsuzawa et al. 2006), and the
aggressiveness of offspring is also influenced by the
aggressiveness of their mothers (Thierry et al. 2004).
The position of an individual in the social network (i.e.,
centrality) largely determines an individual’s behavior with
respect to other members (Sueur et al. 2011a, b). The
maintenance of social relationships in a social network
through grooming behavior is a time-consuming task and,
if the physical cognition of nursery-reared chimpanzees is
impaired, social cognition, particularly the ability to
develop and maintain relationships, may also be impaired.
Social network analysis (SNA) tools are also valuable in
primate behavioral management: in rhesus macaques
(Macaca mulatta), social network measures were shown to
be good predictors of aggressiveness (McCowan et al.
2008). In chimpanzees, SNA allowed the assessment of
social preferences in a captive group, validating the use of
a large modern facility where individuals are not forced to
interact (Clark 2011). Using SNA, another study showed
that, following the successful integration of two adult
groups, chimpanzees choose with whom they wished to
associate and interact via a very gradual process of building
strong affiliative relationships with unfamiliar individuals
(Schel et al. 2013). Social network analysis showed that
central individuals (showing a high betweenness coefficient) in groups of dolphins (Tursiops truncatus) link
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different sub-populations, acting as ‘‘brokers’’ and allowing the transmission of information among the entire
population (Lusseau et al. 2006). In other studies, the
simulated removal of central individuals from a network in
captivity according to decreasing centrality resulted in
greater network fragmentation and loss of group stability
than did the removal of random targets (chimpanzees:
Kanngiesser et al. 2011; mandrills: Bret et al. 2013).
In this study, we assessed whether the grooming
behavior and social centrality of 15 chimpanzees differed
according to their origin: captive-born vs wild-born. We
measured and compared several centrality indices between
wild- and captive-origin members, also considering the
hierarchical rank and age of individuals. We expected
social network centralities to be linked to individual attributes such as age or dominance rank, as shown in Kanngiesser et al. (2011). On the other hand, we expected to
observe differences among individuals according to their
origin, with wild-origin chimpanzees showing greater
social ability with their congeners and displaying higher
centrality. We anticipated homophily according to origin,
with clustering between wild-origin and captive-origin
individuals. Indeed, Massen and Koski (2013) showed that
chimpanzee relationships are based on similarities in
individual characteristics such as personality. We also use
theoretical methods to remove individuals from the social
network and assess the impact of removing either captiveor wild-born members on group stability and cohesiveness.
We hypothesized that group stability would also be better
maintained by wild-origin individuals.
Methods
Subjects and environment
The observed chimpanzees were housed in the Kumamoto
Sanctuary (KS), Japan, in an all-male captive group of 15
individuals, seven of whom were of wild origin and eight
of whom were of captive origin (see Morimura et al. 2011
for more information on the facility and its history). The
captive-born chimpanzees were not all reared maternally.
Four of them were rejected by their mothers within
4 months of birth and subsequently hand-reared. One
individual was separated from its mother at the age of
7 months following the breeding policy of the owner
institute at that time and then hand-reared. All of these
hand-reared individuals were put together with other handreared individuals of similar age into peer groups by 1 year
of age, but two of them (Mi and Ka, see Table 1) were
isolated and kept alone in a cage before 3 years of age,
while three (Ni, Ke, and To) grew up in peer groups with
1–5 members until adulthood. The remaining three
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Table 1 Characteristics and
centrality measures of each
group member studied
Individual
Age
Rank
Origin
Number of yearsa
Ge
33
6
w
1
5
0
8.18
0.03
Go
30
9
w
1
5
0.17
293.77
0.11
Ka
21
2
c
0.3
13
0.2
368.64
0.09
Ke
22
8
c
0.01
8
0.25
509.7
0.08
Le
42
12
w
6
9
0.51
708.3
0.12
Mk
20
3
c
4.3
8
0.12
224.88
0.07
Mt
20
1
c
8.5
10
0.54
757.54
0.09
Mi
22
4
c
0.2
10
0.11
209.28
0.06
Na
31
11
w
2
6
0.07
133.92
0.03
Ni
24
13
c
0.6
9
0.23
437.46
0.09
No
31
7
w
2
Sat
17
5
c
2.2
Degree
Eigenvector
Reach
Clustering
13
0.07
133.76
0.06
9
0.12
222.37
0.1
Sh
30
10
w
1
12
0.44
699.63
0.06
Ta
34
15
w
2
9
0.15
274.6
0.09
To
21
14
c
0.01
4
0.01
14.69
0.04
Rank refers to dominance hierarchy rank. w indicates wild and c indicates captive origin of individuals.
Definitions of centrality measures are given in the methods section
a
Number of years: since wild for wild-origin individuals or since separation from the mother for captiveorigin individuals
individuals (Mk, Mt, and Sat) were mother-reared for at
least the first 2 years, but they were housed as mother–
infant pairs, and did not have contact with other conspecifics. During our study, the chimpanzees had access to
three outdoor enclosures from 9:00 a.m. to 5:00 p.m., and
their group compositions differed each day. That is, the
total of 15 individuals was divided into two or three parties,
based on the divisions between enclosures. Parties consisted either of three groups of five individuals or one
group of five individuals and another of 10. The social
group we studied had been stable for 2 years (no arrival or
departure of individuals). Details of the KS chimpanzees
are summarized in Table 1. Our study was solely observational, and involved no handling or invasive experiments. The chimpanzees were already habituated to human
presence in proximity to their enclosure.
groups because of other activities; Majolo et al. 2008). It is
also useful, as it allows studying the reciprocity of interactions: the direction of grooming is easier to measure than
is that of physical approaches or contacts, and the time a
pair spends grooming is easily measurable using instantaneous sampling. We also used ad libitum recorded pantgrunt data (10 months, records from caretakers and M.L.)
to establish the dominance hierarchy (Landau’s linearity
index, N = 408, h0 = 0.24, p = 0.003; De Vries 1998).
Hierarchical rank was correlated with age (N = 15,
r = 0.59, p = 0.021).
Social network measures
We derived a simple ratio index (Cairns and Schwager
1987) from the behavioral observations as follows:
Xab
;
Xab þ Yab þ Ya þ Yb
Behavioral data
Index ¼
Data were collected from 9:00 a.m. to 4:30 p.m. over
25 days in May–June 2012. We used behavior-dependent
sampling (Altmann 1974) during 20 min sessions, for a
total of 54.5 h of observations. All grooming events were
recorded during a session, including groomer and groomee
identity and duration of grooming (Fig. 1). Grooming
behavior is a useful way to measure the strength of social
relationships in primates, particularly in chimpanzees
(Fedurek and Dunbar 2009). This behavior is a complex
social activity occupying up to 25 % of chimpanzees’
waking hours (grooming time is often limited in wild
where Xab is the proportion of time individuals a and
b were observed grooming together, Yab is the proportion
of time individuals a and b were observed together but not
grooming, and Ya (or Yb) is the proportion of time individual a (or individual b) was observed alone. We obtained
a weighted matrix of interactions and measured from this
network the degree (the number of relationships each group
member has with others), eigenvector (a measure of the
influence of an individual, depending on the strengths of its
relationships but also on the influence of the other group
members with whom he is connected), and reach (a
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Fig. 1 Male chimpanzees
engaging in social grooming at
Kumamoto Sanctuary
measure of the proportion of group members one individual can reach, depending on the number of necessary path
steps) of each individual using Ucinet (Borgatti et al.
2002). We also measured the clustering coefficient,
assessing how the members with whom an individual is
connecting are themselves linked. Global SNA measures
were also calculated: density (the proportion of observed
relationships compared with all possible ones) and the
diameter of the network (longest and shortest path from
one individual to another in the network).
Simulated removal of individuals
After preliminary analyses, we transformed this weighted
matrix into a binary unweighted matrix (0–1) by establishing a threshold, ignoring all values under this threshold
(0), and assigning all remaining values the same weight (1),
as in Kanngiesser et al. (2011). The chosen threshold was
that leading to maximum network modularity (established
with SOCPROG 2.5; Whitehead 2009). We set two other
thresholds (average and average ? one-third standard
deviation; Gilby and Wrangham 2008; Fedurek et al.
2013), but we obtained similar results as with the maximum modularity threshold. Thus, we present only the
results with the maximum modularity threshold, as this
method is more objective.
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Using Ucinet software (Borgatti et al. 2002), we simulated the removal of individuals from the binary network.
We followed the same protocol as that described in Lusseau (2003) and Flack et al. (2006), and Kanngiesser et al.
(2011). We removed up to seven of the 15 individuals
(50 %), from highest to lowest betweenness (the
betweenness of a node quantifies how many pairs can be
formed using this node as a bridge between two other
nodes). In one simulation, we removed only wild-origin
members, and only captive-origin members were removed
in another. At each step of removal (i.e., each individual
removed), we measured the diameter and density of the
network, the size (the number of group members) of the
largest cluster (the cluster gathering the most members),
and the number of isolated clusters.
Statistical analysis
First, using Mann–Whitney tests, we tested whether the
percentages of total grooming (received and given),
received grooming, and given grooming differed between
captive-born and wild-born individuals.
Next, we used Spearman rank correlation tests to assess
the influence of hierarchical rank, age, and number of years
separated from the mother or since capture on centrality
measures of the weighted network. We used Mann–
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Whitney tests to assess the influence of origin—captive vs
wild—on centrality measures, still on the weighted network. We also measured the effect of origin on changes in
global measures during theoretical removals on the
unweighted network using Kolmogorov–Smirnov tests. We
used Monte Carlo resampling procedures (Berry and
Mielke 2000) for the Spearman rank correlation tests, and
we used exact tests (Good 2005) for the Mann–Whitney
and Kolmogorov–Smirnov tests. All statistical tests were
performed with R 2.8.1 (R Development Core Team,
Hothorn and Everitt 2014]) with a = 0.05.
Results
Influence of origin on grooming
The percentage of total grooming did not differ between
captive-born and wild-born individuals (mediancaptive =
4.82 ± 9.95; medianwild = 5.32 ± 10.02; W = 50,898; p =
0.301). Wild-born individuals neither gave (mediancaptive =
3.54 ± 5.84; medianwild = 2.93 ± 5.33; W = 12,249;
p = 0.221) nor received (mediancaptive = 3.52 ± 6.29;
medianwild = 2.88 ± 4.78; W = 11,574; p = 0.727) more
grooming than captive-born ones.
Influence of individual attributes on centrality
We first tested the amount of grooming performed by
individuals of each origin. The weighted network had a
density of 0.614 and a diameter of 2 (Fig. 2a). Hierarchical
cluster analysis shows three subgroups of five, three, and
two individuals and four individuals not belonging to any
subgroup (Fig. 3). In this way, there is no group division
according to origin. The maximum modularity was 0.43,
and the cophenetic correlation coefficient was 0.89.
Modularity and cophenetic correlation coefficients greater
than about 0.3 and 0.8, respectively, are taken to indicate a
useful division of the population (Newman 2004, 2006).
Centrality measures for each individual are indicated in
Table 1. There was no correlation (Spearman correlation
test) between the hierarchical rank and the degree (r =
–0.37, p = 0.169), the eigenvector (r = -0.06,
p = 0.820), the reach (r = –0.06, p = 0.830), or the
clustering coefficient (r = –0.02, p = 0.939). Similarly,
we found no correlation between the age of individuals
and the degree (r = -0.08, p = 0.780), the eigenvector
(r = –0.08, p = 0.772), the reach (r = -0.08, p = 0.780),
or the clustering coefficient (r = -0.1, p = 0.725).
Centrality measures did not differ between wild- and
captive-origin members regardless of the measure tested
(p C 0.676, U C 24, -0.293 B z B -0.464, Table 2). The
origin of the members had no effect on their integration
into the network. For individuals of captive origin, only the
eigenvector coefficient was correlated with the number of
years separated from the mother (r = 0.72, p = 0.04 vs
r B 0.58, p C 0.132 for all other coefficients). This was
driven primarily by one individual being separated very
late from his mother compared with other group members.
Age at capture for wild-origin individuals was not correlated with any centrality coefficients (r B 0.39,
p C 0.383).
Simulated removals of individuals
The binary network had a density of 0.238 and a diameter
of 3 (Fig. 2b). After removals, changes in the binary network diameter showed no differences between wild-origin
and captive-origin removals (K–S, z = 0.650, p = 0.627).
The fraction of members in the largest cluster changed
significantly during the removals (Fig. 4) for both wild(Wilcoxon signed-rank test, p = 0.013, T = 36) and captive-origin (Wilcoxon signed-rank test, p = 0.0078,
T = 36) removals. However, changes differed according to
the number of removals (K–S, z = –2.21, p = 0.03), and
there was greater variation for wild-origin removals (45 %)
than for captive-origin removals (25 %).
Changes in the number of isolated clusters differed
according to the origin of individuals removed (K–S, z = 1.5,
p = 0.022; Fig. 4). There was a significant change in the
number of isolated clusters when removing wild-origin
members (Wilcoxon signed-rank test, p = 0.014, T = 36),
whereas the number of isolated clusters during captive-origin
removal was stable with no observable changes.
Changes in density differed according to the origin of
individuals removed (K–S, z = 1.5, p = 0.022, Fig. 5).
The density changed significantly during wild-origin
removals (Wilcoxon signed-rank test, p = 0.00078,
T = 36), but was stable during the removal of captiveorigin individuals.
Discussion
The maintenance of captive groups of primates entails
considerable involvement in group management (McCowan et al. 2008; Clark 2011; Dufour et al. 2011). Individuals with deprived early-rearing conditions may have
trouble behaving appropriately in their social groups.
Social network analysis is a way of evaluating the integration of individuals into the group network based on their
centrality and the group’s stability. Here, we wanted to
assess whether an individual’s origin (i.e., wild vs captive)
affected her/his social integration.
Short observation times, a limitation in most studies,
were useful here, as we studied a complex and dynamic
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Fig. 2 a Weighted social networks and, b binary (unweighted) social
networks of grooming interactions in the groups studied. Nodes
represent group members, with larger size indicating higher degrees.
White indicates wild origin, whereas gray indicates captive origin.
The procedure used to binarize the network is described in the
methods section. Graphs were drawn using Gephi 0.8.2 (Bastian et al.
2009)
Fig. 3 Hierarchical cluster
analysis based on the maximum
modularity of the focal
chimpanzee group. Individuals
are named on the right.
Individuals with similar colors
belong to the same subgroup,
except for those denoted in
black, which were solitary
social network. Even if the social network of a chimpanzee
group can be considered stable over some period of time,
changes might still occur. In a captive managed group,
individuals may be added regularly, resulting in position
changes in the social network. The most recent addition to
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the group we studied arrived in 2010, and thus the group
had been stable for 2 years. However, this does not necessarily mean that the social network had been stable for
2 years. Few studies have focused on the temporal
dynamics of social networks, and we had no clear idea of
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the time needed for a social network to stabilize. Therefore,
short-term observations minimized confounding variation
due to social network evolution, which might have otherwise obscured variation due to the wild or captive origin of
members. Moreover, a new chimpanzee was planned to be
added to the group at the end of the observation period,
making it impossible to gather data during this period.
Based on four different network centralities (degree,
eigenvector, reach, and clustering coefficients), chimpanzees did not differ in their network centralities,
regardless of origin. Likewise, they did not differ in time
spent grooming or being groomed. As centrality measures
indicate the power (eigenvector), integration (degree and
reach), or cohesion (clustering) of network members, wildand captive-origin members share similar power repartitioning and integration in this grooming network. They are
similarly connected to others in terms of the quantity of ties
(measured by the degree), the separation from or cohesion
with other members (measured by the reach and clustering
Table 2 Average of centrality measures for captive- and wild-origin
chimpanzees (±standard deviation)
Origin
Degree
Eigenvector
Reach
Clustering
Captive
8.87 ± 2.53
0.19 ± 0.16
343 ± 227
0.08 ± 0.02
Wild
8.43 ± 3.25
0.20 ± 0.20
321 ± 278
0.08 ± 0.04
coefficients), and the connectivity with others (measured
by the eigenvector). If there were differences based on wild
or captive origin, or differences due to the arrival of a new
individual in the social group, they were no longer visible
in the state of network evolution we observed. Indeed,
during our study, group composition had been stable for
2 years, a time that is apparently sufficient for the social
integration of group members. To this end, Schel et al.
(2013) concluded that 1 year is needed for aggression
between newly integrated groups of chimpanzees to subside, although association data still indicated the persistence of two distinct subgroups. Such negative results
might also be due to group composition. The group we
studied was composed of approximately half captive-born
and half wild-born individuals. As a consequence, any
single group member, whatever his origin, had a high
probability of interacting with individuals of both origins,
which might impact social centralities. However, we
hypothesized that captive-born individuals would not be
less attractive to other group members but would instead be
less prone to interacting with their congeners. According to
this hypothesis, we should nonetheless have observed some
differences in centrality according to origin, whatever the
number of individuals per condition. These centralities
could also be strongly affected by other factors, reducing
the effect of origin; however, we found no influence of
hierarchical rank or age on the centrality measures. Several
Fig. 4 Evolution of the size of
the largest cluster and the
number of isolated clusters
during the theoretical removals
of wild-origin (top) and captiveorigin (bottom) members
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Fig. 5 Evolution of network density during theoretical removals
studies of chimpanzees showed a link between hierarchy
and social centrality (Kanngiesser et al. 2011; Rushmore
et al. 2014), with high-ranking individuals having the
highest centrality values. However, high social network
variability seems to exist between chimpanzee groups due
to group composition or the personalities of key individuals
(Van Leeuwen et al. 2013; Cronin et al. 2014). Thus, we
cannot say whether the lack of correlation in our study
group was due to captive conditions, group composition, or
variation in the social network. Schel et al. (2013) also
suggested that some individuals were important in facilitating the integration of other members. This may have
been the case in our group, with one or more individuals
behaving in a way that mitigated the origin effect.
We tested the theoretical removal of individuals on four
measures. Of these, only the diameter remained unchanged
when removing members of captive vs wild origin. For the
other measures, removing individuals of wild origin yielded greater changes in the network than did removing
captive-origin individuals. These removals were based on
the betweenness coefficients of individuals. The betweenness coefficient is a measure of an individual’s function in
group cohesion, linking different subgroups. Lusseau and
Newman (2004) defined these specific individuals in dolphins as ‘‘brokers who act as links between sub-communities and who appear to be crucial to the social cohesion of
the population as a whole.’’ Although we did not find any
differences with respect to the four centrality measures
described above, it appeared that removing wild-origin
individuals with higher betweenness had a greater impact
than did removing those of captive origin. The evolution of
the fraction of members in the largest cluster and of the
number of isolated clusters differed between the wild- and
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captive-origin removals. Density was much more strongly
impacted when removing wild-origin than captive-origin
chimpanzees. The fraction of members in the largest
cluster, the number of isolated clusters, and the density
covaried, with a peak at four wild-origin individuals
removed (30 %). Similar results were obtained using the
same methodology in ground squirrels (Manno 2008) and
in chimpanzees (Kanngiesser et al. 2011): after increasing
or remaining stable, density decreased when additional
individuals were removed because of their low centralities.
Thus, more links are broken by removing wild-origin
individuals than by removing captive-origin ones. Overall,
it seems that, on an individual level, the centrality of wildborn individuals did not differ significantly from that of
captive-born ones but that, at the group level, the former
had a greater impact on network stability.
Our results show that differences may emerge between
individuals being early reared in the wild or in captive
settings. However, the differences we observed were
weaker than we expected and did not seem to impact the
integration of individuals into their groups. Wild-origin
individuals seem, however, to be more important for group
cohesion. We hypothesized that social cognition would be
affected by captive-born conditions. However, in contrast
to the long-term effects on physical cognition (Brent et al.
1995; Morimura and Mori 2010), our results showed that
living in social groups might compensate for the negative
effects of non-natural rearing and that non-natural rearing
did not obviously impair social cognition, notwithstanding
the effect during theoretical removal. One might suggest
that the space was too restricted in our study to observe the
social preferences of chimpanzees (Clark 2011). However,
Fig. 2a highlights variation in the strength of social relationships. Further studies should be undertaken as new
individuals are introduced into the group (Schel et al. 2013)
to observe how social relationships are established and
reorganized according to group member attributes. Nevertheless, it is noteworthy that SNA, and theoretical
removal analysis in particular, was able to highlight differences between individuals that would have been
impossible to show with classical methods. The social
environment of captive animals is important for their wellbeing (McCowan et al. 2008; Asher et al. 2009; Koene and
Ipema 2014), and we are only beginning to understand how
SNA might enhance animal welfare. A better understanding of these topics could help in selecting individuals
before forming new groups of captive animals or identify
socially deprived animals who might benefit from social or
physical cognitive enrichment (Sueur and Pelé 2015).
Acknowledgments We thank all the caretakers at the KS, particularly Michael Seres, for their cooperation and assistance. CS gratefully acknowledges the support of both the University of Strasbourg
Author's personal copy
Primates
Institute for Advanced Study (USIAS) and the Fyssen Foundation.
This study was funded by JSPS KAKENHI Grant Numbers 25119008
and 26245069, MEXT KAKENHI Grant Number 24000001, JSPSLGP-U04, and MEXT-PRI-Human Evolution. Our animal husbandry
and research practices complied with international standards and were
in accordance with the recommendations of the Weatherall report on
the use of non-human primates in research as well the guidelines
issued by the Primate Society of Japan. The study protocol was
approved by the Animal Experimentation Committee of the Wildlife
Research Center, Kyoto University (No. WRC-2014KS001A).c
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